/*
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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/*
 *
 *
 *
 *
 *
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/publicdomain/zero/1.0/
 */

package java.util.concurrent.atomic;

import java.util.function.LongUnaryOperator;
import java.util.function.LongBinaryOperator;
import sun.misc.Unsafe;

/**
 * A {@code long} value that may be updated atomically.  See the
 * {@link java.util.concurrent.atomic} package specification for
 * description of the properties of atomic variables. An
 * {@code AtomicLong} is used in applications such as atomically
 * incremented sequence numbers, and cannot be used as a replacement
 * for a {@link java.lang.Long}. However, this class does extend
 * {@code Number} to allow uniform access by tools and utilities that
 * deal with numerically-based classes.
 *
 * @author Doug Lea
 * @since 1.5
 */
public class AtomicLong extends Number implements java.io.Serializable {

  private static final long serialVersionUID = 1927816293512124184L;

  // setup to use Unsafe.compareAndSwapLong for updates
  private static final Unsafe unsafe = Unsafe.getUnsafe();
  private static final long valueOffset;

  /**
   * Records whether the underlying JVM supports lockless
   * compareAndSwap for longs. While the Unsafe.compareAndSwapLong
   * method works in either case, some constructions should be
   * handled at Java level to avoid locking user-visible locks.
   */
  static final boolean VM_SUPPORTS_LONG_CAS = VMSupportsCS8();

  /**
   * Returns whether underlying JVM supports lockless CompareAndSet
   * for longs. Called only once and cached in VM_SUPPORTS_LONG_CAS.
   */
  private static native boolean VMSupportsCS8();

  static {
    try {
      valueOffset = unsafe.objectFieldOffset
          (AtomicLong.class.getDeclaredField("value"));
    } catch (Exception ex) {
      throw new Error(ex);
    }
  }

  private volatile long value;

  /**
   * Creates a new AtomicLong with the given initial value.
   *
   * @param initialValue the initial value
   */
  public AtomicLong(long initialValue) {
    value = initialValue;
  }

  /**
   * Creates a new AtomicLong with initial value {@code 0}.
   */
  public AtomicLong() {
  }

  /**
   * Gets the current value.
   *
   * @return the current value
   */
  public final long get() {
    return value;
  }

  /**
   * Sets to the given value.
   *
   * @param newValue the new value
   */
  public final void set(long newValue) {
    value = newValue;
  }

  /**
   * Eventually sets to the given value.
   *
   * @param newValue the new value
   * @since 1.6
   */
  public final void lazySet(long newValue) {
    unsafe.putOrderedLong(this, valueOffset, newValue);
  }

  /**
   * Atomically sets to the given value and returns the old value.
   *
   * @param newValue the new value
   * @return the previous value
   */
  public final long getAndSet(long newValue) {
    return unsafe.getAndSetLong(this, valueOffset, newValue);
  }

  /**
   * Atomically sets the value to the given updated value
   * if the current value {@code ==} the expected value.
   *
   * @param expect the expected value
   * @param update the new value
   * @return {@code true} if successful. False return indicates that the actual value was not equal
   * to the expected value.
   */
  public final boolean compareAndSet(long expect, long update) {
    return unsafe.compareAndSwapLong(this, valueOffset, expect, update);
  }

  /**
   * Atomically sets the value to the given updated value
   * if the current value {@code ==} the expected value.
   *
   * <p><a href="package-summary.html#weakCompareAndSet">May fail
   * spuriously and does not provide ordering guarantees</a>, so is
   * only rarely an appropriate alternative to {@code compareAndSet}.
   *
   * @param expect the expected value
   * @param update the new value
   * @return {@code true} if successful
   */
  public final boolean weakCompareAndSet(long expect, long update) {
    return unsafe.compareAndSwapLong(this, valueOffset, expect, update);
  }

  /**
   * Atomically increments by one the current value.
   *
   * @return the previous value
   */
  public final long getAndIncrement() {
    return unsafe.getAndAddLong(this, valueOffset, 1L);
  }

  /**
   * Atomically decrements by one the current value.
   *
   * @return the previous value
   */
  public final long getAndDecrement() {
    return unsafe.getAndAddLong(this, valueOffset, -1L);
  }

  /**
   * Atomically adds the given value to the current value.
   *
   * @param delta the value to add
   * @return the previous value
   */
  public final long getAndAdd(long delta) {
    return unsafe.getAndAddLong(this, valueOffset, delta);
  }

  /**
   * Atomically increments by one the current value.
   *
   * @return the updated value
   */
  public final long incrementAndGet() {
    return unsafe.getAndAddLong(this, valueOffset, 1L) + 1L;
  }

  /**
   * Atomically decrements by one the current value.
   *
   * @return the updated value
   */
  public final long decrementAndGet() {
    return unsafe.getAndAddLong(this, valueOffset, -1L) - 1L;
  }

  /**
   * Atomically adds the given value to the current value.
   *
   * @param delta the value to add
   * @return the updated value
   */
  public final long addAndGet(long delta) {
    return unsafe.getAndAddLong(this, valueOffset, delta) + delta;
  }

  /**
   * Atomically updates the current value with the results of
   * applying the given function, returning the previous value. The
   * function should be side-effect-free, since it may be re-applied
   * when attempted updates fail due to contention among threads.
   *
   * @param updateFunction a side-effect-free function
   * @return the previous value
   * @since 1.8
   */
  public final long getAndUpdate(LongUnaryOperator updateFunction) {
    long prev, next;
    do {
      prev = get();
      next = updateFunction.applyAsLong(prev);
    } while (!compareAndSet(prev, next));
    return prev;
  }

  /**
   * Atomically updates the current value with the results of
   * applying the given function, returning the updated value. The
   * function should be side-effect-free, since it may be re-applied
   * when attempted updates fail due to contention among threads.
   *
   * @param updateFunction a side-effect-free function
   * @return the updated value
   * @since 1.8
   */
  public final long updateAndGet(LongUnaryOperator updateFunction) {
    long prev, next;
    do {
      prev = get();
      next = updateFunction.applyAsLong(prev);
    } while (!compareAndSet(prev, next));
    return next;
  }

  /**
   * Atomically updates the current value with the results of
   * applying the given function to the current and given values,
   * returning the previous value. The function should be
   * side-effect-free, since it may be re-applied when attempted
   * updates fail due to contention among threads.  The function
   * is applied with the current value as its first argument,
   * and the given update as the second argument.
   *
   * @param x the update value
   * @param accumulatorFunction a side-effect-free function of two arguments
   * @return the previous value
   * @since 1.8
   */
  public final long getAndAccumulate(long x,
      LongBinaryOperator accumulatorFunction) {
    long prev, next;
    do {
      prev = get();
      next = accumulatorFunction.applyAsLong(prev, x);
    } while (!compareAndSet(prev, next));
    return prev;
  }

  /**
   * Atomically updates the current value with the results of
   * applying the given function to the current and given values,
   * returning the updated value. The function should be
   * side-effect-free, since it may be re-applied when attempted
   * updates fail due to contention among threads.  The function
   * is applied with the current value as its first argument,
   * and the given update as the second argument.
   *
   * @param x the update value
   * @param accumulatorFunction a side-effect-free function of two arguments
   * @return the updated value
   * @since 1.8
   */
  public final long accumulateAndGet(long x,
      LongBinaryOperator accumulatorFunction) {
    long prev, next;
    do {
      prev = get();
      next = accumulatorFunction.applyAsLong(prev, x);
    } while (!compareAndSet(prev, next));
    return next;
  }

  /**
   * Returns the String representation of the current value.
   *
   * @return the String representation of the current value
   */
  public String toString() {
    return Long.toString(get());
  }

  /**
   * Returns the value of this {@code AtomicLong} as an {@code int}
   * after a narrowing primitive conversion.
   *
   * @jls 5.1.3 Narrowing Primitive Conversions
   */
  public int intValue() {
    return (int) get();
  }

  /**
   * Returns the value of this {@code AtomicLong} as a {@code long}.
   */
  public long longValue() {
    return get();
  }

  /**
   * Returns the value of this {@code AtomicLong} as a {@code float}
   * after a widening primitive conversion.
   *
   * @jls 5.1.2 Widening Primitive Conversions
   */
  public float floatValue() {
    return (float) get();
  }

  /**
   * Returns the value of this {@code AtomicLong} as a {@code double}
   * after a widening primitive conversion.
   *
   * @jls 5.1.2 Widening Primitive Conversions
   */
  public double doubleValue() {
    return (double) get();
  }

}
